1. Field of the Invention
The present invention relates to exposure control in an electronic still camera.
2. Related Background Art
In a photographing system employing conventional silver halide film, the photographing operation with flash has been conducted by regulating the lens diaphragm and the shutter speed at suitable values, causing a flash unit to emit light, integrating the amount of light reflected from the object with light integrating means simultaneously with said light emission and automatically interrupting the light emission of the flash unit by a light sensor provided in the camera or the flash unit when the amount of light reaches a value for obtaining an optimum exposure.
However the amount of light from the flash unit is limited, and it may be insufficient for obtaining optimum exposure for example because the object is too distant from the flash unit or the aperture of the lens diaphragm is adjusted too small. In order to predict such situation prior to the photographing operation, there has been required a preparatory operation such as precise calculation of photographing conditions by the operator, or automatic in-camera operation of irradiating the object with infrared light to simulate the actual light emission from the flash unit, thereby identifying whether the amount of light from the flash unit and the lens diaphragm are suitable for photographing.
However the former operation requires detailed knowledge of the operator on the camera operation, takes time and is cumbersome. On the other hand, the latter operation requires a complex and expensive apparatus. Also if such operation identifies the amount of light from the flash unit as insufficient, it has been required to alter the photographing conditions, to employ a more sensitive photographic film or to use a more powerful flash unit. For these reasons, in most photographing operations, such prior checking has not been conducted, but, if the amount of exposure is not enough due to the insufficient amount of light from the flash unit, alarm means on the camera is activated to inform the operator of such insufficient amount of light, thereby causing the operator to take the photograph again under readjusted conditions. However such system is very defective, because an image unsuitable for viewing is inevitably recorded in such case, and the opportunity of photographing may be easily lost.
The above-mentioned drawbacks of wasting a frame and losing the opportunity of photographing also exist when the object is too close. In such case the film may be exposed excessively as the interruption of light emission from the flash unit may be delayed due to the delay in the function of the control circuit of the flash unit.
Electronic still cameras have had similar problems in the use with a flash unit, as disclosed in U.S. Pat. No. 4,366,501. Since the latitude of exposure is narrower than in the conventional silver halide film, the problem of excessive or deficient amount of light from the flash unit is more serious, and a satisfactory solution for this problem has been heeded.